So I got my stamp a couple days ago so I took my SBR build out to test fire.  It was almost magical.  It fires great.  Accuracy is superb. The only thing bad was I kept getting random BHO.  It held open on an empty mag every time...but sometimes would just randomly hold open with rounds still in the mag.  

Anyone have similar issues?  Ideas?

QC10 Small Glock Lower
JP Bolt
JP 9mm Silent Capture
VLTOR MUR
ADCO 5" Barrel

I dunno, dude, but I'll but I'll bump this to the top.

take the lower off the gun.  take a magazine you use and load a few rounds into it.  insert the mag into the lower.  the bolt hold open lever should not rise.  the little tab near the front that activates on the glock magazine folower most likely needs to be tweaked ever so slightly up.  now do that and then assemble the rifle.  put an empty magazine in the rifle and rack the charging handle.  the bolt should be caught and held back.  if that still works after you slightly tweaked the tab then you should probably be good to go.  with a loaded mag in the gun the bho lever should still be sitting flush in the channel in the lower.

hope that helps

did you install the little spring that came with the QC10 or a factory spring for BHO lever?

if he had installed the factory spring most liely the glock mag follower would not have enough force to activate the bolt hold open.  if you installed the qc10 spring it may be a touch too short and cause the lever to "rattle or shift up mid firing.  does the bolt hold open return to rest position with the hammer cocked or does it wiggle?

It's not moving with a loaded mag inserted.



Yup I installed the QC10 spring.



I think this is the problem because it does wiggle and seems loose.  I am going to pop off the bho and try lengthening the spring a tad.

Thank you for the help.  I'll report back on my findings.

My money is on this.  Small steps. Just enough tension to return to neutral. Every bit past that the glock mag has to overcome it.  And if you didn't notice this system has an extremely shitty short stick for leverage.

Subscribed. I have the same exact problem as O.P.

Are you using Glock magazines or aftermarket?  Is the magazine catch keeping your magazines solidly locked in?  What sort of load are you seeing these random bolt catch activations with?  HOW ARE YOU HOLDING THE GUN?

Glock 30rd mags, couple different gen mags, no aftermarket mags.  Mags are locked in solid. I had issues with some of my 124gr hand loads as well as some factory 124gr ammo.

After looking over the lower and thinking about it, I was also concerned about how I was holding it.  I thought maybe I was hitting it with my palm.  I shot some with my support hand on the lower and some on the fore-end, I can't remember if it happened only when my hand was on the lower.  That would be pretty embarrassing if it was my mechanics causing the problem.  I really don't think that was the cause but, I can not rule it out as I haven't had a chance to make it back out to the range yet.

It might not be your grip, but it's a possibility.  Anther possibility might be that your silent buffer/spring isn't right for the bolt and ammo you're using.  If you have a standard carbine spring and buffer, I'd take that to the range with me, and maybe some Winchester White Box 115 gr 9mm as well.

If it's not your grip actively touching something, it could be that the gun is bouncing too much with the blowback/recoil from heavier loads.  Unless your silent buffer/spring is supposed to be particularly heavy, it might not be heavy enough - a LOT of people insist in really heavy buffers for their 9mm ARs because it smooths out the blowback action and (usually) keeps the buffer from hitting the back of the receiver extension very hard.  Lighter factory rounds instead of your 125 grain factory and handloaded rounds, so a standard buffer system should feel smoother overall as well.  If it was the bolt slamming into the back of the extension that sometimes triggered the BHO, a heavier buffer or lighter loads should at least reduce the frequency of your random bolt catches.

I had this exact problem, and it's definitely annoying (especially in full auto).  In the long DDLES thread, Red-Rx7 posted a set of instructions on how to adjust the BHO (link, scroll about halfway down the page).  I played with it for a while and got it to run, but never completely to my satisfaction.  Ultimately I decided BHO wasn't that important to me so I removed the "transfer bar" (for lack of a better term) completely.  The bolt no longer locks open on the last round, but then again it doesn't lock open during a magazine either.  Since the original BHO lever is there I can still manually lock the bolt open.

Mad-Machinist from Macon Armory has been working with QC10 and designed a replacement BHO device which you'll be able to retrofit to existing guns.  I'll take a look at that when he comes out with it, but in the mean time I'll just run without one.

-bob

My issue is definitely cause by pressure on the mag.  If any rearward pressure is put on the mag it engages the BHO.  I tweaked the bar a little and got it to work better but, it's still unreliable.  I think I will remove it and wait for the retrofit part as well.  It shoots brilliantly except for the BHO.  I tested with a number different gr rounds, so I don't feel my particular issue with ammo related.  It was happening with them all when I put any kind of pressure on the mag.

that should not happen.  the activating tab that gets pushed on the follower needs to be adjusted.  put a full mag in and take the upper off. rock the mag back and forth and see where the magazine is hitting the lever and adjust it accordingly.  my guess is the short tab needs to be tweaked up ever so slightly

Got it working good then after a couple mags the BHO catch split in two..  

Meh, I'll just run it without I guess.

thats why I run slash's 9mm buffers.

Stack $1.75 worth of quarters behind the buffer spring.
The goal is to allow the bolt rearward
Only far enough to lock back on empty mag.